Dr. M.ANEEQUE ALAM
Department of Anesthesiology
Pain is unpleasant sensory and
emotional experience associated
with actual or potential tissue
damage, or described in terms of
Ref: International Association for the Study of Pain(IASP)
o Pain is SUBJECTIVE phenomena
Nocioception is a complex sequence of actions
between tissue damage and the perception of
Transduction: Translation of a (chemical) pain
stimulus into electrical activity on nerve level.
Transmission: Guidance of the pain – information
through the nervous system, including:
Primary afferent nerve-ends that go to the dorsal horn of
the spinal cord.
ascending (inter-) neurons that project their information
from the spinal cord to the brainstem and
The thalamic-cortical pathways
Modulation: Modification of the nociceptive
transmission through a number of humoral and
Perception: Observing the pain in
a conscious way. Integration of transduction,
transmission and modulation with the unique
psychology of the individual, resulting in a
subjective and emotional pain sensation
PAIN IS CLASSIFIED INTO NOCICEPTIVE, NEUROPATHIC AND
1. Nociceptive is pain caused by tissue damage (inflammation)
which stimulate pain receptors (nociceptors).
2. Neuropathic: (pain due to injury of nerve pathway)
site of injury: Central Central pain (thalamic infarct).
Mixed Plexus avulsion, Post herpetic neuralgia.
Peripheral Neuroma, nerve compression, phantom, neuralgias.
character: burning, tingling, numbness, pressing, squeezing, itching, constant +/-
intermittent shooting, lancinating, electric.
3. Psychogenic: (difficult to differentiate whether secondary to or actual
cause of pain), anxiety, depression (30% of depressives complain of pain on initial
Nociceptors are special receptors that
respond only to noxious stimuli and generate
nerve impulses which the brain interprets as “pain”
Free nerve endings
oNon adaptive it’s a
to keep the individual
trying to remove the
damaging stimulus or
to get away from it.
CHARACTERISTICS A DELTA FIBRES C-FIBRES
CONDUCTION SPEED FAST(70-120 m/sec) SLOW(0.2-2 m/sec)
DURATION BRIEF LONG
RECEPTIVE FIELD SMALL LARGE
LOCALIZATION PRECISE DIFFUSE
SENSORY QUALITY SHARP,PRICKING ACHING,DULL,
CNS RESPONSE RELFEX,ANALYSIS EMOTIONAL,
FAST PAIN SLOW PAIN
onset: during application of the stimulus Shortly after application if tissue damage
Duration: short duration Longer duration
Nature: pricking Burning
Afferent: A-delta fibers C-fibers
Neurotransmitter: glutamate Substance-P
Significance: * determine site & severity.
* Initiate withdrawal reflexes.
Associated with arousal, autonomic &
Localization: well-localized Poorly-localized
THE NEUROCHEMICALS OF PAIN
• Glutamate - Central
• Substance P - Central
• Brandykinin - Peripheral
• Prostaglandins - Peripheral
PAIN’S ASCENDING PATHWAY TO THE
THREE neurons from the receptor
to the cerebral cortex
First order neuron:
Cell body located in the
dorsal root ganglion.
Starts from free nerve ending
Ends at substantia gelatinosa
Second order neuron:
Has cell body in the
spinal cord or
• Starts from substantia
Axon decussate &
Terminate on 3rd order
Third order neuron:
Has cell body in thalamus
Axon terminates on
cerebral cortex ipsilaterally
The Descending Pathway
pain afferents stimulates the neurons in
periaqueductal gray (PAG) - gray matter
surrounding the cerebral aqueduct in the
midbrain results in activation of efferent anti-nociceptive
from there the impulses are transmitted
through the spinal cord to the dorsal horn
there thay inhibit or block transmission of
nociceptive signals at the level of dorsal horn
Melzack & Wall (1965)
. non-painful input closes
the "gates" to painful input
APPLICATIONS OF GATE THEORY
Stimulation of touch fibres for pain relief:
TENS (transcutaneous electrical nerve
It is the maximum intensity of pain can be tolerated by the
subject without obvious complaint.
Pain tolerance is affected by a number of factors:
- Anxiety, depression & fatigue ------> pain tolerance.
- rest, sever exercise & strong emotional excitement ------> pain tolerance.
Increased pain from a stimulus that
normally provokes pain
Pain due to a stimulus that does not
normally provoke pain.
PAIN FELT AWAY FROM THE ORIGINAL SITE OF THE
o sensations are described as
perceptions that an individual experiences
relating to a limb or an organ that is not
physically part of the body
o brain contains neuromatrix of the
body image –neurosignature like a